GRL

Uranus is one of the least explored planets in our solar system, it exhibits a unique magnetic field structure which was observed by NASA's Voyager 2 mission nearly 50 years ago. Notably, Uranus displays extreme magnetic field asymmetry, a feature exclusive to the icy giants. We use the Boris algorithm to investigate how high energy protons behave within this unusual magnetic field, which is motivated by Voyager 2's observation of lower-than-expected high energy proton radiation belt intensities at Uranus. When considering full drift motions of high energy protons around Uranus, the azimuthal drift velocity can vary by as much as 15% around the planet. This results in areas around Uranus where particles will be more depleted (faster drift) and other regions where there is a surplus of particles (slower drift). This could provide a partial explanation for the “weak” proton radiation belts observed by Voyager 2.

The plasma density is one of the most fundamental quantities of any plasma yet measuring it in space is exceptionally difficult when the density is low. Measurements from particle detectors are contaminated by spacecraft photoelectrons and methods using plasma wave emissions are hampered by natural plasma instabilities which dominate the wave spectrum. Here we present a new method which calculates the density from magnetosonic waves near the lower hybrid resonance frequency. The method works most effectively when the ratio of the plasma to cyclotron frequency is fpe/fce < 3.5. The method provides a lower bound on the plasma density. Using the new method we show that wave acceleration of electrons to relativistic energies is increased by orders of magnitude. The method enables years of satellite data to be re-analyzed for the Earth and the effectiveness of wave acceleration at the Earth, Jupiter and Saturn to be re-assessed.

The evolution of gas hydrates influenced by the seawater environment is unknown. We present a model of structural transformation from sI hydrate to sII hydrate due to the influence of seawater environment and vent fluid in nature through in situ experiments of gas hydrate formation in the Haima cold seep area. The in situ experimental results indicate that gas hydrates preferentially form as sI hydrates even in cold seep environments where C2+ hydrocarbons are present. During subsequent evolution, the sI hydrates could restructured at the effect of seawater environment and vent fluid, causing transformation to sII hydrates under the influence of hydrate stability. The supply of gas and direct contact with seawater environment are critical factors for structural transformation. Such structural transformation is the result of gas hydrates seeking thermodynamic stability and may be common in active cold seep areas.

Understanding the generation of damaging, high-frequency ground motions during earthquakes is essential both for fundamental science and for effective hazard preparation. Various theories exist regarding the origin of high-frequency ground motions, including the standard paradigm linked to slip heterogeneity on the rupture plane, and alternative perspectives associated with fault complexity. To assess these competing hypotheses, we measure ground motion amplitudes in different frequency bands for 3 ≤ M ≤ 5.8 earthquakes in Southern California and compare them to empirical ground motion models. We utilize a Bayesian inference technique called the Integrated Nested Laplace Approximation (INLA) to identify earthquake source regions that produce higher or lower ground motions than expected. Our analysis reveals a strong correlation between fault complexity measurements and the high-frequency ground motion event terms identified by INLA. These findings suggest that earthquakes on complex faults (or fault networks) lead to stronger-than-expected ground motions at high frequencies.

Leveraging Gravity Recovery and Climate Experiment mascon products spanning from April 2002 to September 2023, we, for the first time, ascertain the substantial influence of cryospheric mass variations on Earth's Chandler wobble (CW). Further, in contrast to traditional analysis conducted in the excitation domain, this study focuses on the polar motion domain and incorporates the wavelet analysis technique. Our findings reveal some intriguing phenomena: Between 2006 and 2020, the cryosphere contributed an average amplitude of approximately 4.85 mas to CW, equivalent to 5.05%, with its impact escalating to about 11 mas from 2018 to 2022, representing a fourfold rise in its contribution ratio to approximately 20%. This marked surge can be attributed to the more erratic glacier mass balance results from ongoing climate change. Moreover, there is a pronounced decrease in the CW signal post-2018, which starkly contrasts with cryospheric contribution, suggesting a potential linkage to climate change yet warrants further investigation.

The interdecadal variability of tropical cyclone precipitation (TCP) over the western North Pacific (WNP) has not been thoroughly explored in previous studies. Here, we show that the TCP variations are modulated by both the Atlantic Multidecadal Oscillation (AMO) and Interdecadal Pacific Oscillation (IPO) as evidenced by reanalysis data and model experiments. A clustering analysis of tropical cyclone tracks shows that the AMO dominates a dipole pattern of TCP anomalies in the South China Sea and along the coastal eastern China. Meanwhile, the IPO dominates TCP over the southeastern WNP. Further analyses show that the AMO, particularly its extratropical component, affects TCP over the WNP by triggering an eastward-propagating Rossby-wave train, resulting in a pair of anomalous gyres over the WNP. Contrastly, the IPO modulates TCP by stimulating tropical circulation anomalies via the tropical pathway. These findings shed light on improving near-term TCP forecast and its regional influence on East Asia.

A minequake of magnitude M L 4.1 occurred on 18 May 2020 early in the morning at the LKAB underground iron ore mine in Kiruna, Sweden. This is the largest mining-induced earthquake in Scandinavia. It generated acoustic signals observed at three infrasound arrays at 9.3 (KRIS, Sweden), 155 (IS37, Norway), and 286 km (ARCI, Norway) distance. We perform full-waveform focal mechanism inversion based on regional seismic data and local infrasound data. These independently highlight that this event was dominated by a shallow-depth collapse in agreement with in-mine seismic station data. However, regional infrasound data cannot inform the inversion process without an accurate model of atmospheric winds and temperatures. Yet, our numerical simulations demonstrate a potential of using local and regional infrasound data to constrain an event's focal mechanism and depth.

The MMS satellites traversed a ∼6 di-wide and ∼500 km/s southward reconnection exhaust at the dayside magnetopause on 6 December 2015 and ∼29 di from the associated X-line region. A narrow ∼0.26–0.34 di layer of enhanced ±3.5 nW/m3 oscillating energy conversion perpendicular to the magnetic field resides in this exhaust. It contained two regions of diverging in-plane electric fields in general agreement with two clockwise electron flow vortices and a proposed increase of the electron vorticity ∇ × V e. The layer developed sunward of a unipolar Hall magnetic field for a duskward BM/BL ∼ 0.9 guide field. Each electron flow vortex supported a local ∆BM ∼ 10 nT strengthening of this Hall field. The presence of this electron-scale layer in a southward exhaust for a duskward guide field is consistent with a two-dimensional simulation of a similar structure that evolved from an X-line into a northward exhaust for a similar strength dawnward guide field.

We obtain three-dimensional models of crustal shear-wave velocity and radial anisotropy in the Bohai Bay basin (BBB), revealing distinct radial anisotropy patterns. The western region of the basin exhibits pronounced positive crustal radial anisotropies, attributed to upper mantle convection driven by the subduction of the Pacific plate during the early Tertiary. Conversely, the eastern region of the basin demonstrates weak to negative radial anisotropies, indicating a compression shear rupture system influenced by the far-field India-Eurasian collision during the Neogene-Quaternary. These differences suggest that the formation of the BBB is associated with the dynamic transition from Pacific subduction to India-Eurasian collision during the Cenozoic. Moreover, the Luxi uplift, with its stable upper-middle crustal structures, acts as a barrier hindering the eastward extension of the BBB.

Despite intensified efforts to better quantify Internal Tide dynamics over past decades, large uncertainties remain regarding their distribution and lifecycle in the ocean. In particular, internal tide incoherence (loss of time-regularity) has limited our ability to characterize, understand, and predict internal tides, challenging the exploitation of new-generation wide-swath satellite altimeters. Based on a realistic high-resolution numerical simulation, we quantify the internal tide distribution and incoherence properties in the North Atlantic. We quantify IT incoherence for sea level and surface currents, and for different vertical modes independently. Our results show that typical decorrelation timescale induced by the mesoscale turbulence are rather short—below 25 days for the first vertical mode. It further exhibits a strong dependence of the internal tide incoherence with location, reflecting regions of enhanced eddy activity, and with vertical mode number—higher baroclinic modes being much more incoherent with shorter decorrelation timescale.

Surface, aircraft, and satellite measurements indicate pervasive early cold season (Augut–September) CO2 emissions across Arctic regions, consistent with increased ecosystem metabolism in plants and soils. A key remaining question is whether cold season sources will become large enough to permanently shift the Arctic into a net carbon source. Polar orbiting GHG satellites provide robust estimation of regional carbon budgets but lack sufficient spatial coverage and repeat frequency to track sink-to-source transitions in the early cold season. Mission concepts such as the Arctic Observing Mission (AOM) advocate for flying imaging spectrometers in highly elliptical orbits (HEO) over the Arctic to address sampling limitations. We perform retrieval and flux inversion simulation experiments using the AURORA mission concept, leveraging a Panchromatic imaging Fourier Transform Spectrometer (PanFTS) in HEO. Our simulations demonstrate the potential benefits of increased CO2 sampling for detecting emissions during the early cold season.

Machine Learning (ML) is having a profound impact in the domain of Weather and Climate Prediction. A recent development in this area has been the emergence of fully data-driven ML prediction models which routinely claim superior performance to that of traditional physics-based models. We examine some aspects of the forecasts produced by three of the leading current ML models, Pangu-Weather, FourCastNet and GraphCast, with a focus on their fidelity and physical consistency. The main conclusion is that these ML models are not able to properly reproduce sub-synoptic and mesoscale weather phenomena and lack the fidelity and physical consistency of physics-based models and this has impacts on the interpretation of their forecasts and their perceived skill. Balancing forecast skill and physical realism will be an important consideration for future ML models.

Accurate wildfire forecasting can inform regional management and mitigation strategies in advance of fire occurrence. Existing systems typically use fire danger indices to predict landscape flammability, based on meteorological forecasts alone, often using little or no direct information on land surface or vegetation state. Here, we use a vegetation characteristic model, weather forecasts and a data-driven machine learning approach to construct a global daily ∼9 km resolution Probability of Fire (PoF) model operating at multiple lead times. The PoF model outperforms existing indices, providing accurate forecasts of fire activity up to 10 days in advance, and in some cases up to 30 days. The model can also be used to investigate historical shifts in regional fire patterns. Furthermore, the underlying data driven approach allows PoF to be used for fire attribution, isolating key variables for specific fire events or for looking at the relationships between variables and fire occurrence.

The long-term memory of the ocean makes sea surface temperature anomalies (SSTAs) become a significant predictor for the subsequent atmosphere, and the tropical ocean is primarily regarded as a major source of atmospheric anomalies. While in North Pacific, the local midlatitude SSTAs also have large contributions but have not been adequately considered yet. We discover a strong connection between the Kuroshio-Oyashio Extension (KOE) SSTAs in spring and the local atmospheric circulation anomalies in following summer at interannual timescale, wherein, the spring KOE SSTAs are generally independent of tropical ocean, and they are primarily induced by the concurrent atmospheric anomalies via surface heat flux and ocean dynamic processes. The spring KOE SSTAs can persist to summer, and then generate nearly reversed whole-layer atmospheric circulation anomalies in their north side through both diabatic heating and atmospheric transient eddy forcing. Consequently, precipitation anomalies in Pan-Pacific regions are distinctly modulated from spring to summer.

Rising temperatures entail important changes in the soil hydrologic processes of the northern permafrost zone. Using the ICON-Earth System Model, we show that a large-scale thaw of essentially impervious frozen soil layers may cause a positive feedback by which permafrost degradation amplifies the causative warming. The thawing of the ground increases its hydraulic connectivity and raises drainage rates which facilitates a drying of the landscapes. This limits evapotranspiration and the formation of low-altitude clouds during the snow-free season. A decrease in summertime cloudiness, in turn, increases the shortwave radiation reaching the surface, hence, temperatures and advances the permafrost degradation. Our simulations further suggest that the consequences of a permafrost cloud feedback may not be limited to the regional scale. For a near-complete loss of the high-latitude permafrost, they show significant temperature impacts on all continents and northern-hemisphere ocean basins that raise the global mean temperature by 0.25 K.

The trade winds cause strong upwelling in the eastern equatorial Pacific, and create the eastern Pacific Cold Tongue (EPCT) that has far-reaching impacts on global climate. However, large discrepancies persist in quantifying 20th-century EPCT sea surface temperature (SST) changes across different instrumental data sets. Here we synthesize four coral Sr/Ca-SST records from the tropical central-eastern Pacific to develop a Cold Tongue Index (CTI) reconstruction for 1887–1997. The coral CTI record shows a rapid 20th century warming of the EPCT, suggesting an underestimation of warming trends in instrumental CTI records. The decadal to multidecadal changes in reconstructed EPCT SST show an association with the Walker Circulation. Our reconstruction indicates that recent EPCT cooling during the global warming hiatus is not unusual in the context of the 20th century. Our results provide new evidence for 20th century EPCT SST changes and an observational constraint for predicting future tropical climate changes.

Central Afar is shaped by the interaction between the Red Sea (RS) and Gulf of Aden (GoA) rifts. While there have been several studies conducted in the region, we know surprisingly little about the mechanism of connection between these two rift branches. Here we use high-resolution 3D lithospheric scale geodynamic modeling to capture the evolution of linkage between the RS and GoA rifts in central Afar. Our results demonstrate that the two rifts initially overlap and interact across a broad zone of faulting and vertical axis block rotation. However, through time, rift overlap is abandoned in favor of direct linkage which generates a series of localized en-echelon basins. The present-day direct linkage between the two rifts is supported by geodetic observations. Our study reconciles previously proposed models for the RS and GoA rift connection by considering spatial and temporal evolution of the rifts.

Accurate modeling of snow depth (SD) processes is critical for understanding global energy balance changes, affecting climate change mitigation strategies. This study evaluates the Coupled Model Intercomparison Project Phase 6 (CMIP6) model performance in simulating daily SD across Canada. We assess CMIP6 outputs against observed data, focusing on daily SD averages, snow cover durations, and rates of accumulation and depletion, alongside annual SD peaks for 11 major Canadian catchments. Our findings reveal that CMIP6 simulations generally overestimate daily SD by 57.7% and extend snow cover duration by 30.5 days on average. While three models (CESM2, UKESM1-0-LL and MIROC6) notably align with observed annual SD peaks, simulation biases suggest the need for enhanced model parameterization to accurately capture snow physics, particularly in regions with permanent snow cover and complex terrains. This analysis underscores the necessity of refining CMIP6 simulations and incorporating detailed geographical data for better SD predictions.

Bedload sediment transport plays an important role in the evolution of rivers, marshes and deltas. In these aquatic environments, vegetation is widespread, and plant species have unique morphology. However, the impact of real plant morphology on flow and sediment transport has not been quantified. This study used model plants with real plant morphology, based on the aquatic species Phragmites australis, Acorus calamus and Typha latifolia. The frontal area of these species increases away from the bed, which leads to higher near-bed velocity than would be predicted from depth-average frontal area. A plant morphology coefficient was defined to quantify the impact of vertically-varied plant frontal area. Laboratory experiments confirmed that the plant morphology coefficient improved the prediction of near-bed velocity, near-bed turbulent kinetic energy and bedload transport rate in canopies with realistic morphology. Plant morphology can alter transport rates by up to an order of magnitude, relative to the assumption of uniform morphology.

Global climate models (GCMs) are unable to produce detailed runoff conditions at the basin scale. Assumptions are commonly made that dynamical downscaling can resolve this issue. However, given the large magnitude of the biases in downscaled GCMs, it is unclear whether such projections are credible. Here, we use an ensemble of dynamically downscaled GCMs to evaluate this question in the Sierra-Cascade mountain range of the western US. Future projections across this region are characterized by earlier seasonal shifts in peak flow, but with substantial inter-model uncertainty (−25 ± 34.75 days, 95% confidence interval (CI)). We apply the emergent constraint (EC) method for the first time to dynamically downscaled projections, leading to a 39% (−28.25 ± 20.75 days, 95% CI) uncertainty reduction in future peak flow timing. While the constrained results can differ from bias corrected projections, the EC is based on GCM biases in historical peak flow timing and has a strong physical underpinning.